Until recently, scientists were puzzled why an earthquake of only 7.5 magnitude caused a devastating tsunami that killed over 2,000 people on the island of Sulawesi in Indonesia in September of 2018. The earthquake didn’t even trigger the tsunami early warning system as normally a tsunami of the size (wave height up to 11m or 36 ft) would require an 8.4 or higher magnitude earthquake. A new study published in the journal Pure and Applied Geophysics has found that the cause of the tsunami was actually a marine landslide in Palu Bay on the west coast of Sulawesi. A combination of computer modeling and observation of the actual sea level data from the event was used to reach their conclusion. They observed a wave period that was very short, consistent with the 3 to 4 minutes expected based on the modeling of a marine landslide compared to the 15 to 60 minute periods for an earthquake-induced tsunami.
A massive landslide has destroyed at least a quarter-mile of State Route 410 in Washington State, about 10 miles from Naches in Yakima County. It has also damaged about 12 structures including residential homes and quarry buildings and diverted the Naches River. The media has been referring to it as the Naches Slide, but the personnel from the Washington Department of Natural Resources, Division of Geology and Earth Resources who have began investigating the slide as well as WSDOT are calling it the Nile Landslide. (Photo by WAStateDNR-DoGaER)
Click through for photos and videos. For more info on the slide, check out the Sliding Thought Blog, an unofficial blog by Isabelle Sarikhan of the WAStateDNR – Division of Geology and Earth Resources “aka” the Washington Geologic Survey. She’s been actively investigating the slide along with some colleagues.